This invention relates to curing fluoropolymer compositions having nitrogen-containing cure-site components.
Fluorine-containing polymers (also known as xe2x80x9cfluoropolymersxe2x80x9d) are a commercially useful class of materials. Fluoropolymers include, for example, crosslinked fluoroelastomers, uncrosslinked fluoroelastomer gums, semi-crystalline fluoroplastics, and or glassy fluoroplastics. Fluoroplastics are generally of high thermal stability and are particularly useful at high temperatures. They may also exhibit extreme toughness and flexibility at very low temperatures. Some have very low dielectric loss and high dielectric strength, and may have unique low friction properties.
Fluoroelastomers exhibit significant tolerance to high temperatures and harsh chemical environments. Consequently, they are particularly well-adapted for use as seals, gaskets, and other molded parts in systems that are exposed to elevated temperatures and/or corrosive chemicals. Such parts are widely used in the chemical processing, semiconductor, aerospace, and petroleum industries, among others.
Fluoroelastomers often include a cure-site component to facilitate cure in the presence of a catalyst. One class of useful cure-site components includes nitrogen-containing monomers. Organotin catalysts are typically used as cure catalysts. Such catalysts, however, are toxic and can leave undesirable extractable metal residues in the cured product.
In one aspect, the invention relates to a composition that includes (a) a fluoropolymer having interpolymerized units derived from a nitrogen-containing cure site monomer, and (b) a catalyst composition that includes a compound having the general formula: 
wherein the group HA is an inorganic or organic acid, e.g., HCl, HNO3, C7F15COOH, and wherein R1, R2, and R3 are each, independently, the same or different alkyl groups having from 1 to about 20 carbon atoms, which may be cyclic or heterocyclic, and one R group may instead be a bond to another R group such that the nitrogen is bonded to or part of an alkenyl, cycloalkenyl, or aromatic group. The substituents may also be olefinic, e.g., mono, di, and trialkyl amine salts, and pyridine salts. R1, R2, and R3 may be fluorinated groups such as Rf(CH2)xxe2x80x94 wherein Rf is a C1-C8 linear or branched and at least partially fluorinated (i.e., fluorinated or perfluorinated) alkylene, cycloalkylene, or oxyalkylene, and x is 1 to 4 (more preferably 1 or 2). Examples of catalyst compositions include compounds of the formula: 
wherein m and n are, independently, 2 to 20.
When a compound has more than one nitrogen atom, the mono, di, and higher salts are also useful.
The composition may further include a second catalyst composition comprising a compound having the formula R1C(OR2)xe2x95x90NH, and salts thereof, where R1 and R2 are, independently, a substituted or unsubstituted C1-C20 (preferably C1-C10, more preferably C1-C7) alkyl, aryl, aralkyl, alkenyl, cycloalkyl, or cycloalkenyl group.
In other aspects, the invention provides a method for curing this composition, as well as curable and cured articles comprising these compositions.
The compositions retain the advantages of the use of nitrogen-containing cure site monomers such as the high temperature performance properties and chemical resistance typically achieved when organotin compounds are used as the catalyst system with such cure site monomers. At the same time, the compositions exhibit markedly improved compression set values. The compositions are useful in applications where polymer stability (e.g., thermal stability) and/or chemical resistance are important. They are also useful in silicon wafer fabrication.
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and from the claims.